Advanced computer architectures may employ multiple processors. Some advanced computer architectures may employ multiple microprocessors on one silicon chip. In a typical application, two microprocessors may be implemented on a single silicon chip, and the implementation may be referred to as a dual core processor. Two or more of the multiple microprocessors may operate in a lock step mode, meaning that each of the lock stepped microprocessors process the same code sequences, and should, therefore, produce identical outputs.
FIG. 1 is a diagram of a prior art dual core processor that uses lock step techniques to improve overall reliability. In FIG. 1, a computer system 18 includes a dual core processor 20 having a single silicon chip 21, on which are implemented microprocessor core 22 and microprocessor core 24. To employ lock step, each of the microprocessor cores 22 and 24 process the same code streams. The cores 22 and 24 are coupled to a lock step logic 26. An event that causes a loss of lock step can occur on either or both of the microprocessor cores 22 and 24. An example of such an event is a data cache error. A loss of lock step, if not promptly corrected, may cause the computer system 18 to “crash” or be “disabled.” In addition, because the microprocessor cores 22 and 24 are running the same code sequence, by definition, communications between the microprocessor cores 22 and 24 may not be possible without causing a loss of lock step. For example, the usual means for communication between processors involves load and store sequences, which must be different between two processors, and which consequently will cause a loss of lock step.